14.21 Line Truncation

As an alternative to continuation (see Continuation Lines),
Emacs can display long lines by truncation. This means that all
the characters that do not fit in the width of the screen or window do
not appear at all. On graphical displays, a small straight arrow in
the fringe indicates truncation at either end of the line. On text
terminals, this is indicated with ‘$’ signs in the leftmost
and/or rightmost columns.

Horizontal scrolling automatically causes line truncation
(see Horizontal Scrolling). You can explicitly enable line
truncation for a particular buffer with the command M-x
toggle-truncate-lines. This works by locally changing the variable
truncate-lines. If that variable is non-nil, long lines
are truncated; if it is nil, they are continued onto multiple
screen lines. Setting the variable truncate-lines in any way
makes it local to the current buffer; until that time, the default
value, which is normally nil, is in effect.

If a split window becomes too narrow, Emacs may automatically enable
line truncation. See Split Window, for the variable
truncate-partial-width-windows which controls this.